Work machine

ABSTRACT

Detection accuracy of a device for obtaining a position of a blade is improved. A motor grader includes an antenna for reception of a satellite position determination signal arranged in a roof portion of a cab, a first IMU mounted on the cab, a second IMU mounted on a draw bar, a rotation angle sensor that detects an angle of rotation of a swing circle with respect to the draw bar, an inclination angle sensor that detects an angle of inclination of a blade with respect to the swing circle, and a controller. The controller obtains the position of the blade in a global coordinate system based on the satellite position determination signal received by the antenna and results of detection by the first IMU, the second IMU, the rotation angle sensor, and the inclination angle sensor.

TECHNICAL FIELD

The present disclosure relates to a work machine.

BACKGROUND ART

U.S. Pat. No. 10,428,493 (PTL 1) discloses a technique for a motor grader including at least one global navigation satellite system (GNSS) antenna and at least one inertial measurement unit (IMU), in which a position of a blade is calculated based on a result of measurement by them and the blade is automatically controlled based on the calculated position thereof.

CITATION LIST Patent Literature

PTL 1: U.S. Pat. No. 10,428,493

SUMMARY OF INVENTION Technical Problem

For highly efficient and high-quality land grading works by a motor grader, desirably, a position of a blade is more accurately obtained. Therefore, improved accuracy in detection by various antennas and sensors for obtaining the position of the blade has been demanded.

The present disclosure proposes a work machine that can achieve improved accuracy in detection by a device for obtaining a position of a blade.

Solution to Problem

According to the present disclosure, a work machine is proposed. The work machine includes a vehicular body frame including a front frame and a rear frame pivotably coupled to the front frame. The work machine includes a cab which an operator enters, the cab being mounted on the vehicular body frame, a draw bar coupled to the front frame, the draw bar being swingable with respect to the front frame, a swing circle supported on the draw bar, the swing circle being rotatable relatively to the draw bar, and a blade supported on the swing circle, the blade being inclined with respect to the swing circle. The work machine includes an antenna for reception of a satellite position determination signal arranged in a roof portion of the cab, a first sensor mounted on the cab, the first sensor detecting an inclination of the cab, a second sensor that detects an angle of inclination of the draw bar with respect to the cab, a third sensor that detects an angle of rotation of the swing circle with respect to the draw bar, and a fourth sensor that detects an angle of inclination of the blade with respect to the swing circle. The work machine includes a controller that obtains a position of the blade in a global coordinate system based on the satellite position determination signal received by the antenna and results of detection by the first sensor, the second sensor, the third sensor, and the fourth sensor.

Advantageous Effects of Invention

According to the work machine in the present disclosure, accuracy in detection by a device for obtaining a position of a blade can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically showing a construction of a motor grader based on an embodiment.

FIG. 2 is a side view of the motor grader shown in FIG. 1 .

FIG. 3 is a diagram illustrating overview of a construction of a pivot mechanism.

FIG. 4 is a plan view of the motor grader with a front frame being pivoted with respect to a rear frame.

FIG. 5 is a perspective view of the motor grader, with a portion around a work implement being shown as being enlarged.

FIG. 6 is a perspective view of the motor grader at an angle different from an angle in FIG. 5 .

FIG. 7 is a block diagram showing a configuration involved with obtainment of a position of a blade, of the motor grader shown in FIG. 1 .

FIG. 8 is a flowchart showing a flow of processing for calculating a position of the blade.

DESCRIPTION OF EMBODIMENTS

An embodiment will be described below with reference to the drawings. In the description below, the same elements have the same reference characters allotted and their labels and functions are also the same. Therefore, detailed description thereof will not be repeated.

FIG. 1 is a perspective view schematically showing a construction of a motor grader 1 based on an embodiment. FIG. 2 is a side view of motor grader 1 shown in FIG. 1 .

As shown in FIGS. 1 and 2 , motor grader 1 based on the embodiment mainly includes a front wheel 11 which is a running wheel, a rear wheel 12 which is a running wheel, a vehicular body frame 2, a cab 3, and a work implement 4. Front wheel 11 includes one wheel on each of left and right sides. Rear wheel 12 includes two wheels on each of left and right sides. Though the figure shows running wheels including two front wheels 11, one on each side, and four rear wheels 12, two on each side, the number and arrangement of front wheels and rear wheels are not limited as such.

Motor grader 1 includes components such as an engine arranged in an engine compartment 6. Work implement 4 includes a blade 42. Motor grader 1 can do such works as land-grading works, snow removal works, light cutting, and mixing of materials with blade 42.

In the description of the drawings below, a direction in which motor grader 1 travels in straight lines is referred to as a fore/aft direction of motor grader 1. In the fore/aft direction of motor grader 1, a side where front wheel 11 is arranged with respect to work implement 4 is defined as the fore direction. In the fore/aft direction of motor grader 1, a side where rear wheel 12 is arranged with respect to work implement 4 is defined as the rear direction. A lateral direction or a side of motor grader 1 is a direction orthogonal to the fore/aft direction in a plan view. A right side and a left side in the lateral direction in facing front are defined as a right direction and a left direction, respectively. An upward/downward direction of motor grader 1 is a direction orthogonal to the plane defined by the fore/aft direction and the lateral direction. A side in the upward/downward direction where the ground is located is defined as a lower side and a side where the sky is located is defined as an upper side.

In the drawings, the fore/aft direction is shown with an arrow X in the drawings, the lateral direction is shown with an arrow Y in the drawings, and the upward/downward direction is shown with an arrow Z in the drawings.

Vehicular body frame 2 shown in FIGS. 1 and 2 extends in the fore/aft direction. Vehicular body frame 2 includes a rear frame 21 and a front frame 22. Rear frame 21 is arranged in the rear of front frame 22. Rear frame 21 supports an exterior cover 25 and components such as an engine arranged in engine compartment 6. Exterior cover 25 covers engine compartment 6. For example, rear wheels 12, two on each side, are attached to rear frame 21 as being rotationally drivable by driving force from the engine.

Front frame 22 is arranged in front of rear frame 21. Front frame 22 has a rear end coupled to a front end of rear frame 21. Rear frame 21 is pivotably coupled to front frame 22. For example, front wheels 11, one on each side, are rotatably attached to front frame 22.

A counterweight 51 is attached to a front end of vehicular body frame 2. Counterweight 51 is an exemplary attachment attached to front frame 22. Counterweight 51 is attached to front frame 22 in order to increase downward load applied to front wheel 11 to enable steering and to increase pressing load onto blade 42.

Motor grader 1 can perform an articulation operation for pivoting front frame 22 with respect to rear frame 21. Motor grader 1 includes a pivot mechanism for performing the articulation operation. FIG. 3 is a diagram illustrating overview of a construction of the pivot mechanism.

As shown in FIG. 3 , front frame 22 and rear frame 21 are coupled to each other by a coupling shaft 53. Coupling shaft 53 extends in the upward/downward direction (a direction perpendicular to the sheet plane in FIG. 3 ). Coupling shaft 53 is arranged below cab 3 (not shown in FIG. 3 ).

Coupling shaft 53 couples front frame 22 to rear frame 21 as being pivotable with respect to rear frame 21. Front frame 22 is revolvable in two directions with respect to rear frame 21 with coupling shaft 53 being defined as the center. An angle formed by front frame 22 with respect to rear frame 21 is adjustable. FIG. 4 is a plan view of motor grader 1 with front frame 22 being pivoted with respect to rear frame 21. FIG. 4 shows a state that front frame 22 has pivoted to the right with respect to rear frame 21.

A centerline CL shown in FIG. 2 represents a center of pivot (center of articulation) of front frame 22 with respect to rear frame 21. Centerline CL is a straight line that passes through a center of coupling shaft 53 and extends in the upward/downward direction. In FIGS. 3 and 4 , centerline CL is a straight line that passes through the center of coupling shaft 53 and extends in a direction perpendicular to the sheet plane.

Front frame 22 pivots with respect to rear frame 21 as a result of extending and retracting of an articulation cylinder 54 coupled between front frame 22 and rear frame 21 based on an operation from cab 3. An angle sensor 58 is attached to rear frame 21, and the angle sensor detects an angle of articulation representing an angle of pivot of front frame 22 with respect to rear frame 21.

By pivoting (articulating) front frame 22 with respect to rear frame 21, a radius of revolution in revolution of motor grader 1 can be made smaller and a ditch digging work or a grading work by offset running can be done. Offset running refers to linear travel of motor grader 1 by setting a direction of pivot of front frame 22 with respect to rear frame 21 and a direction of revolution of front wheel 11 with respect to front frame 22 to directions opposite to each other.

Referring back to FIGS. 1 and 2 , cab 3 is carried on front frame 22. Cab 3 includes an indoor space which an operator enters and it is arranged at the rear end of front frame 22. Cab 3 may be carried on rear frame 21.

An operator's seat 31 where the operator in cab 3 sits is arranged in cab 3. Operator's seat 31 is arranged substantially in the center of cab 3 in the fore/aft direction and the lateral direction. Cab 3 includes a roof portion 3R that covers the cab from above operator's seat 31 and a plurality of pillars that support roof portion 3R. Roof portion 3R is arranged above operator's seat 31. Each pillar is coupled to a floor portion and roof portion 3R of cab 3.

Cab 3 has a highly rigid structure in conformity with a roll-over protective structure (ROPS) standardized as ISO 3471 and a falling-object protective structure (FOPS) standardized as ISO 3449. For protection of an operator in cab 3 even in the event of roll-over of motor grader 1 or falling of a falling object on cab 3, deformation of cab 3 is effectively suppressed.

In front of operator's seat 31 of cab 3, a steering wheel 33 for an operator to perform an operation to steer motor grader 1 is arranged. Steering wheel 33 is attached to a steering console 34 and supported on steering console 34. By operating steering wheel 33, an orientation of front wheel 11 can be changed so that motor grader 1 can change its direction of travel. In cab 3, such operation portions as a gear shift lever, a control lever for work implement 4, a brake, and an accelerator pedal are provided.

In roof portion 3R of cab 3, an antenna 60 for reception of a satellite position determination signal is arranged. Antenna 60 protrudes upward from roof portion 3R. Antenna 60 is attached to roof portion 3R which is a position in motor grader 1 highest in the upward/downward direction while blade 42 is not erected, and arranged further higher than roof portion 3R.

A first inertial measurement unit (IMU) 61 is mounted on cab 3. First IMU 61 is arranged in a ceiling portion of the indoor space in cab 3. First IMU 61 is arranged directly under antenna 60. Antenna 60 and first IMU 61 are arranged at positions superimposed on each other when motor grader 1 is viewed in a plan view.

Antenna 60 and first IMU 61 are arranged in a front edge portion of cab 3. Antenna 60 and first IMU 61 are arranged in front of operator's seat 31. Antenna 60 and first IMU 61 are arranged directly above steering console 34. Steering console 34, and antenna 60 and first IMU 61 are arranged at positions superimposed on one another when motor grader 1 is viewed in the plan view. Antenna 60 and first IMU 61 are arranged in front of centerline CL which is the center of pivot of front frame 22 with respect to rear frame 21.

Work implement 4 mainly includes a draw bar 40, a swing circle 41, blade 42, a swing motor 49, and various cylinders 44 to 48. FIG. 5 is a perspective view of motor grader 1, with a portion around work implement 4 being shown as being enlarged. FIG. 6 is a perspective view of motor grader 1 at an angle different from an angle in FIG. 5 .

Draw bar 40 is arranged below front frame 22. Draw bar 40 has a front end swingably coupled to a tip end portion of front frame 22 by a ball shaft portion 402. Draw bar 40 has a rear end supported on front frame 22 with a pair of lift cylinders 44 and 45 being interposed. Lower ends of piston rods of lift cylinders 44 and 45 are attached to draw bar 40. As the pair of lift cylinders 44 and 45 extends and retracts in synchronization, the rear end of draw bar 40 can move up and down with respect to front frame 22. As lift cylinders 44 and 45 extend and retract differently from each other, draw bar 40 can swing up and down with an axis along a direction of travel of a vehicle being defined as the center.

A draw bar shift cylinder 46 is attached to front frame 22 and a side end of draw bar 40. As draw bar shift cylinder 46 extends and retracts, the rear end of draw bar 40 can move laterally with respect to front frame 22.

Swing circle 41 is arranged below front frame 22. Swing circle 41 is arranged below draw bar 40. Swing circle 41 is supported on the rear end of draw bar 40. Swing motor 49 is, for example, a hydraulic motor. Swing circle 41 can swingably be driven by swing motor 49 clockwise or counterclockwise with respect to draw bar 40 when viewed from above the vehicle. Swing circle 41 is rotatable relatively to draw bar 40. As swing circle 41 is swingably driven, an angle of inclination of blade 42 with respect to front frame 22 in a plan view is adjusted.

A swivel joint 43 is arranged at a center of swing of swing circle 41. A hydraulic pressure is sent from draw bar 40 to swing circle 41 with swivel joint 43 being interposed.

Blade 42 is supported on swing circle 41. Blade 42 is supported on front frame 22 with swing circle 41 and draw bar 40 being interposed.

A blade shift cylinder 47 is attached to swing circle 41 and blade 42 and arranged along a longitudinal direction of blade 42. With blade shift cylinder 47, blade 42 is movable in the longitudinal direction thereof with respect to swing circle 41.

A tilt cylinder 48 is attached to swing circle 41 and blade 42. As a result of extending and retracting of tilt cylinder 48, blade 42 swings around the axis extending in the longitudinal direction thereof with respect to swing circle 41, and can change its orientation in the upward/downward direction. Tilt cylinder 48 can change an angle of inclination of blade 42 with respect to the direction of travel of the vehicle.

As set forth above, blade 42 is constructed to be able to move up and down with respect to the vehicle, swing around the axis along the direction of travel of the vehicle, change an angle of inclination with respect to the fore/aft direction, move in the longitudinal direction thereof, and swing around the axis extending in the longitudinal direction thereof, with draw bar 40 and swing circle 41 being interposed.

A second inertial measurement unit (IMU) 62 is mounted on draw bar 40. A rotation angle sensor that detects an angle of rotation of swing circle 41 with respect to draw bar 40 is arranged on swivel joint 43. A stroke sensor that detects a cylinder length of draw bar shift cylinder 46 is attached to draw bar shift cylinder 46. A stroke sensor that detects a cylinder length of blade shift cylinder 47 is attached to blade shift cylinder 47. A stroke sensor that detects a cylinder length of tilt cylinder 48 is attached to tilt cylinder 48.

FIG. 7 is a block diagram showing a configuration involved with obtainment of a position of blade 42, of motor grader 1 shown in FIG. 1 . As shown in FIG. 7 , motor grader 1 includes a controller 70. Controller 70 is, for example, a main controller that controls the entire motor grader 1, and includes a central processing unit (CPU), a non-volatile memory, and a timer.

Antenna 60 receives radio waves (GNSS radio waves) from a satellite and outputs a signal in accordance with the received radio waves to controller 70.

First IMU 61 detects an inclination of cab 3. First IMU 61 detects an angle of inclination of cab 3 with respect to the fore/aft direction, the lateral direction, and the upward/downward direction. In the construction in the embodiment where cab 3 is mounted on front frame 22, first IMU 61 can also be said as detecting an angle of inclination of vehicular body frame 2 (front frame 22) with respect to the fore/aft direction, the lateral direction, and the upward/downward direction. First IMU 61 outputs a result of detection of the inclination of cab 3 to controller 70. First IMU 61 mounted on cab 3 corresponds to the first sensor in the embodiment that detects the inclination of cab 3.

Second IMU 62 detects an inclination of draw bar 40. Second IMU 62 detects an angle of inclination of draw bar 40 with respect to the fore/aft direction, the lateral direction, and the upward/downward direction. Second IMU 62 outputs a result of detection of the angle of inclination of draw bar 40 to controller 70. The angle of inclination of draw bar 40 with respect to cab 3 is found based on a result of detection by first IMU 61 and a result of detection by second IMU 62. Second IMU 62 corresponds to the second sensor in the embodiment that detects the angle of inclination of draw bar 40 with respect to cab 3.

Blade tilt stroke sensor 63 is a stroke sensor attached to tilt cylinder 48. Blade tilt stroke sensor 63 detects a cylinder length of tilt cylinder 48. Blade tilt stroke sensor 63 outputs a result of detection of the cylinder length of tilt cylinder 48 to controller 70. An angle of inclination of blade 42 with respect to swing circle 41 is found based on the cylinder length of tilt cylinder 48 detected by blade tilt stroke sensor 63. Blade tilt stroke sensor 63 corresponds to the fourth sensor in the embodiment that detects an angle of inclination of blade 42 with respect to swing circle 41.

Circle rotation sensor 64 is attached onto swivel joint 43. Circle rotation sensor 64 corresponds to the third sensor in the embodiment that detects an angle of rotation of swing circle 41 with respect to draw bar 40. Circle rotation sensor 64 outputs a result of detection of the angle of rotation of swing circle 41 to controller 70.

Blade shift stroke sensor 65 is a stroke sensor attached to blade shift cylinder 47. Blade shift stroke sensor 65 detects a cylinder length of blade shift cylinder 47. Blade shift stroke sensor 65 outputs a result of detection of the cylinder length of blade shift cylinder 47 to controller 70. An amount of movement of blade 42 with respect to swing circle 41 in the longitudinal direction of blade 42 is found based on the cylinder length of blade shift cylinder 47 detected by blade shift cylinder 47.

Controller 70 includes a storage unit 72, a global coordinate computation unit 74, a detection information obtaining unit 76, and a blade position calculator 78.

A program for controlling various operations of motor grader 1 is stored in storage unit 72. Controller 70 performs various types of processing for controlling operations of motor grader 1 based on the program stored in storage unit 72. Storage unit 72 is a non-volatile memory and provided as an area where necessary data is stored.

Positions relative to first IMU 61 (which are referred to as draw bar attachment portion reference positions below), of draw bar attachment portion position pair (P1 and P2; see FIGS. 1 and 5 ) which is cylinder root positions where left and right lift cylinders 44 and 45 are attached to draw bar 40 when a position of draw bar 40 with respect to front frame 22 is neutral are stored in storage unit 72. Positions relative to draw bar attachment portion position pair P1 and P2 (which are referred to as blade opposing-end reference positions below), of blade lower-edge opposing-end position pair (P11 and P12; see FIGS. 1, 5, and 6 ) which is positions of opposing ends of a lower edge of blade 42 in the longitudinal direction of blade 42 when the position of swing circle 41 with respect to draw bar 40 is neutral, the position of blade 42 inclined with respect to swing circle 41 is neutral, and the position of blade 42 that carries out reciprocating motion with respect to swing circle 41 in the longitudinal direction of blade 42 is neutral, are stored in storage unit 72.

Global coordinate computation unit 74 computes a current position of antenna 60 in the global coordinate system based on a satellite position determination signal inputted from antenna 60. The global coordinate system refers to a three-dimensional coordinate system expressed by a latitude, a longitude, and an altitude, with the Earth being defined as the reference. An absolute position of antenna 60 in the global coordinate system is defined by coordinate data of the latitude, the longitude, and the altitude of antenna 60.

Detection information obtaining unit 76 obtains information detected by each of first IMU 61, second IMU 62, blade tilt stroke sensor 63, circle rotation sensor 64, and blade shift stroke sensor 65. Detection information obtaining unit 76 obtains the inclination of cab 3, the inclination of draw bar 40, the cylinder length of tilt cylinder 48, the angle of rotation of swing circle 41, and the cylinder length of blade shift cylinder 47.

Blade position calculator 78 calculates a position of blade 42 in the global coordinate system based on the position of antenna 60 in the global coordinate system computed by global coordinate computation unit 74 and the information obtained by detection information obtaining unit 76.

FIG. 8 is a flowchart showing a flow of processing for calculating a position of blade 42. A method of specifying a position of blade 42 in the global coordinate system will be described with reference to FIG. 8 .

In step S1, the current position of antenna 60 in the global coordinate system is computed. Global coordinate computation unit 74 computes coordinate data of the latitude, the longitude, and the altitude of antenna 60 based on a satellite position determination signal inputted from antenna 60.

In step S2, the current position of first IMU 61 in the global coordinate system is computed. Each of antenna 60 and first IMU 61 is mounted on cab 3. Positions of antenna 60 and first IMU 61 relative to each other are constant regardless of an operation of motor grader 1. Therefore, the current position of first IMU 61 in the global coordinate system is obtained by computation based on the current position of antenna 60 in the global coordinate system and the positions of antenna 60 and first IMU 61 relative to each other.

In step S3, detection information from each sensor is obtained. Detection information obtaining unit 76 obtains detection information on the inclination of cab 3 from first IMU 61. Detection information obtaining unit 76 obtains detection information on the inclination of draw bar 40 from second IMU 62. Detection information obtaining unit 76 obtains detection information on the cylinder length of tilt cylinder 48 from blade tilt stroke sensor 63. Detection information obtaining unit 76 obtains detection information on the angle of rotation of swing circle 41 from circle rotation sensor 64. Detection information obtaining unit 76 obtains detection information on the cylinder length of blade shift cylinder 47 from blade shift stroke sensor 65.

In step S4, current draw bar attachment portion position pair P1 and P2 relative to first IMU 61 are computed.

Blade position calculator 78 receives information on a result of detection by first IMU 61 and a result of detection by second IMU 62, from detection information obtaining unit 76. Blade position calculator 78 calculates a current angle of inclination of draw bar 40 with respect to cab 3 based on the angle of inclination of cab 3 with respect to the fore/aft direction, the lateral direction, and the upward/downward direction and the angle of inclination of draw bar 40 with respect to the fore/aft direction, the lateral direction, and the upward/downward direction.

In order to more accurately detect the angle of inclination of draw bar 40 with respect to cab 3, in addition to the results of detection by first IMU 61 and second IMU 62, the cylinder length of draw bar shift cylinder 46 detected by the stroke sensor attached to draw bar shift cylinder 46 may be used.

Blade position calculator 78 obtains current draw bar attachment portion position pair P1 and P2 relative to first IMU 61 by calculation based on the draw bar attachment portion reference positions read from storage unit 72 and the current angle of inclination of draw bar 40 with respect to cab 3.

In step S5, current blade lower-edge opposing-end position pair P11 and P12 relative to draw bar attachment portion position pair P1 and P2 are calculated.

Blade position calculator 78 receives information on a result of detection by circle rotation sensor 64, from detection information obtaining unit 76. Blade position calculator 78 obtains the angle of rotation of swing circle 41 with respect to draw bar 40. Blade 42 rotates as being integrated with swing circle 41, relatively to draw bar 40. Blade position calculator 78 obtains the angle of rotation of blade 42 with respect to draw bar 40.

Blade position calculator 78 receives information on the result of detection of the cylinder length of tilt cylinder 48, from detection information obtaining unit 76. Blade position calculator 78 obtains the angle of inclination of blade 42 with respect to swing circle 41.

Blade position calculator 78 receives information on the result of detection of the cylinder length of blade shift cylinder 47, from detection information obtaining unit 76. Blade position calculator 78 obtains an amount of movement of blade 42 with respect to swing circle 41 in the longitudinal direction of blade 42.

Blade position calculator 78 obtains current blade lower-edge opposing-end position pair P11 and P12 relative to draw bar attachment portion position pair P1 and P2 by computation based on the blade opposing-end reference positions read from storage unit 72, as well as the current angle of rotation of blade 42 with respect to draw bar 40, the current angle of inclination of blade 42 with respect to swing circle 41, and the current amount of movement of blade 42 with respect to swing circle 41 in the longitudinal direction of blade 42.

In step S6, blade position calculator 78 obtains current draw bar attachment portion position pair P1 and P2 in the global coordinate system by calculation based on the current position of first IMU 61 in the global coordinate system and the current positions of first IMU 61 and draw bar attachment portion position pair P1 and P2 relative to each other. Blade position calculator 78 obtains current blade lower-edge opposing-end position pair P11 and P12 in the global coordinate system by calculation based on the current position of first IMU 61 in the global coordinate system, current draw bar attachment portion position pair P1 and P2 relative to first IMU 61, and current blade lower-edge opposing-end position pair P11 and P12 relative to draw bar attachment portion position pair P1 and P2. Blade position calculator 78 obtains a current position in the upward/downward direction in the global coordinate system, of a straight line that connects blade lower-edge opposing-end position pair P11 and P12 to each other.

The position of the lower edge of blade 42 in the global coordinate system thus obtained can be used for automatic control of motor grader 1. Motor grader 1 can be controlled to travel, for example, by control of blade 42 such that the lower edge of blade 42 coincides with a position of a designed surface in the upward/downward direction during land grading works. Motor grader 1 can be controlled to travel by control of blade 42 such that one of blade lower-edge opposing-end position pair P11 and P12 coincides with a toe of a slope of design topography during slope shaping works. Through such automatic control, motor grader 1 can do highly efficient and high-quality works.

Characteristic features and functions and effects of the present embodiment will be summarized as below, although some description may overlap with the description above.

As shown in FIG. 2 , motor grader 1 in the embodiment includes antenna 60 for reception of a satellite position determination signal arranged in roof portion 3R of cab 3 and first IMU 61 mounted on cab 3.

By arranging antenna 60 in roof portion 3R of cab 3 which is a position highest in the vehicular body of motor grader 1, influence by an obstacle nearby is lessened and hence antenna 60 can readily catch the satellite position determination signal. Since both of antenna 60 and first IMU 61 are arranged in highly rigid cab 3, an error between the position of antenna 60 and the position of first IMU 61 due to deflection of the vehicular body is lessened. In addition, antenna 60 and first IMU 61 are arranged at positions close to each other. Thus, the current position of first IMU 61 in the global coordinate system can accurately be obtained based on the current position of antenna 60 in the global coordinate system and the current position of first IMU 61 relative to antenna 60.

Therefore, current blade lower-edge opposing-end position pair P11 and P12 in the global coordinate system can accurately be obtained based on the current position of first IMU 61 in the global coordinate system and current blade lower-edge opposing-end position pair P11 and P12 relative to first IMU 61.

As shown in FIG. 2 , first IMU 61 is arranged in the ceiling portion of the indoor space in cab 3. With such arrangement, first IMU 61 can reliably be arranged at a position close to antenna 60 arranged in roof portion 3R.

As shown in FIG. 2 , first IMU 61 is arranged directly below antenna 60. With such arrangement, first IMU 61 can be arranged at a position closer to antenna 60.

As shown in FIG. 2 , first IMU 61 is arranged in the front edge portion of cab 3. By arranging first IMU 61 in the front edge portion which is a position in cab 3 close to blade 42, an error of blade lower-edge opposing-end position pair P11 and P12 relative to first IMU 61 due to deflection of the vehicular body can be lessened. Therefore, current blade lower-edge opposing-end position pair P11 and P12 in the global coordinate system can more accurately be obtained. In addition, since a larger indoor space can be secured in cab 3, a degree of freedom in arrangement of components provided in cab 3 such as operator's seat 31 can be improved, and comfort and workability of an operator in cab 3 can be improved.

As shown in FIG. 2 , first IMU 61 is arranged in front of operator's seat 31 in cab 3. First IMU 61 can thus reliably be arranged in the front edge portion of cab 3.

As shown in FIG. 2 , first IMU 61 is arranged directly above steering console 34. First IMU 61 can thus reliably be arranged in the front edge portion of cab 3.

As shown in FIG. 2 , cab 3 is mounted on front frame 22. When cab 3 is mounted on rear frame 21, in order to obtain blade lower-edge opposing-end position pair P11 and P12 relative to first IMU 61 mounted on cab 3, correction of an angle of articulation is required. When cab 3 is mounted on front frame 22, correction of the angle of articulation is not required and an error involved with this correction can be lessened. Therefore, current blade lower-edge opposing-end position pair P11 and P12 in the global coordinate system can more accurately be obtained.

As shown in FIG. 2 , first IMU 61 is arranged in front of centerline CL which is the center of pivot of front frame 22 with respect to rear frame 21. With such arrangement, first IMU 61 can reliably be arranged in the front edge portion of cab 3 close to blade 42.

In the description of the embodiment, an example of use of results of detection by blade tilt stroke sensor 63, circle rotation sensor 64, and blade shift stroke sensor 65 for obtaining blade lower-edge opposing-end position pair P11 and P12 relative to draw bar attachment portion position pair P1 and P2 is described. Blade shift stroke sensor 65 does not necessarily have to be provided in blade shift cylinder 47. On the premise that the position of blade 42 with respect to swing circle 41 in the longitudinal direction thereof is neutral, the position of blade 42 may automatically be controlled. An operator may manually perform an operation to steer motor grader 1 while the operator looks at the position of blade 42. An operation to steer motor grader 1 may automatically be controlled, and in this case, a rotation sensor that detects a steering angle of front wheel 11 may additionally be provided.

Instead of first IMU 61 and second IMU 62, an attitude heading reference system may be employed. By attaching the attitude heading reference system capable of measuring a yaw angle to each of cab 3 and draw bar 40, an amount of shift in the lateral direction of draw bar 40 with respect to front frame 22 (with respect to cab 3) can clearly be detected. Since the cylinder length of draw bar shift cylinder 46 does not have to supplementarily be used for improving accuracy in detection of the angle of inclination of draw bar 40 with respect to cab 3 and the stroke sensor does not have to be provided in draw bar shift cylinder 46, the construction can be simplified.

A sensor for obtaining an angle of inclination of blade 42 with respect to swing circle 41 is not limited to blade tilt stroke sensor 63. Instead of blade tilt stroke sensor 63, a third IMU or an inclination sensor may be attached to blade 42 so that the angle of inclination of blade 42 with respect to swing circle 41 may be obtained from a result of detection by second IMU 62 and a result of detection by the third IMU or the inclination sensor.

A plurality of antennas 60, a plurality of first IMUs 61, and a plurality of IMUs 62 may be provided. By using results of detection by the plurality of antennas and the plurality of IMUs, the position of blade 42 in the global coordinate system can more accurately be specified. Furthermore, reliability of a configuration for specifying the position of blade 42 in the global coordinate system can be improved.

In order to obtain the position in the upward/downward direction, of the lower edge of blade 42 in the global coordinate system, two points in the lower edge of blade 42 different from blade lower-edge opposing-end position pair P11 and P12 may be detected. For example, two points which are a central position and an end position in the longitudinal direction of blade 42 in the lower edge of blade 42 may be detected. By using blade lower-edge opposing-end position pair P11 and P12, a distance between two points is maximized so that accuracy in detection of the position of blade 42 can be improved.

Antenna 60 does not necessarily have to protrude upward from a roof surface of cab 3. Antenna 60 may be embedded in roof portion 3R of cab 3. By shielding antenna 60, collision of an obstacle with antenna 60 and resultant lowering in accuracy in detection by antenna 60 can be suppressed.

Antenna 60 may be arranged at a position other than the front edge portion of cab 3. For example, antenna 60 may be arranged in a rear edge portion of cab 3. First IMU 61 may be arranged at a position other than the ceiling portion of cab 3. First IMU 61 may be arranged at a position other than the front edge portion of cab 3. For example, first IMU 61 may be arranged in the rear of operator's seat 31.

It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

1 motor grader; 2 vehicular body frame; 3 cab; 3R roof portion; 4 work implement; 11 front wheel; 12 rear wheel; 21 rear frame; 22 front frame; 31 operator's seat; 33 steering wheel; 34 steering console; 40 draw bar; 41 swing circle; 42 blade; 43 swivel joint; 44, 45 lift cylinder; 46 draw bar shift cylinder; 47 blade shift cylinder; 48 tilt cylinder; 49 swing motor; 53 coupling shaft; 54 articulation cylinder; 58 angle sensor; 60 antenna; 61 first inertial measurement unit; 62 second inertial measurement unit; 63 blade tilt stroke sensor; 64 draw bar shift stroke sensor; 65 circle rotation sensor; 66 blade shift stroke sensor; 70 controller; 72 storage unit; 74 global coordinate computation unit; 76 detection information obtaining unit; 78 blade position calculator; 402 ball shaft portion; CL centerline 

1. A work machine comprising: a vehicular body frame including a front frame and a rear frame pivotably coupled to the front frame; a cab which an operator enters, the cab being mounted on the vehicular body frame; a draw bar coupled to the front frame, the draw bar being swingable with respect to the front frame; a swing circle supported on the draw bar, the swing circle being rotatable relatively to the draw bar; a blade supported on the swing circle, the blade being inclined with respect to the swing circle; an antenna for reception of a satellite position determination signal arranged in a roof portion of the cab; a first sensor mounted on the cab, the first sensor detecting an inclination of the cab; a second sensor that detects an angle of inclination of the draw bar with respect to the cab; a third sensor that detects an angle of rotation of the swing circle with respect to the draw bar; a fourth sensor that detects an angle of inclination of the blade with respect to the swing circle; and a controller that obtains a position of the blade in a global coordinate system based on the satellite position determination signal received by the antenna and results of detection by the first sensor, the second sensor, the third sensor, and the fourth sensor.
 2. The work machine according to claim 1, wherein the first sensor is arranged in a ceiling portion of the cab.
 3. The work machine according to claim 1, wherein the first sensor is arranged directly under the antenna.
 4. The work machine according to claim 1, wherein the first sensor is arranged in a front edge portion of the cab.
 5. The work machine according to claim 4, wherein the cab includes an operator's seat where an operator takes a seat, and the first sensor is arranged in front of the operator's seat.
 6. The work machine according to claim 4, wherein the cab includes a steering wheel for an operator to perform an operation for steering the work machine and a steering console on which the steering wheel is supported, and the first sensor is arranged directly above the steering console.
 7. The work machine according to claim 1, wherein the cab is mounted on the front frame.
 8. The work machine according to claim 7, wherein the first sensor is arranged in front of a center of pivot of the front frame with respect to the rear frame. 